Module 18 - Signals & Communications
Morse, Sound and Light Signals
What you will learn
Separate Morse SOS, a safe-water mark's Morse A and COLREG manoeuvring or warning blasts by purpose, context and observation.
Similar short and long patterns belong to different systems. A signal is useful only when the learner knows whether it indicates distress, identifies an aid to navigation or communicates manoeuvre and doubt in sight of another vessel.
SOS in Morse is three short, three long, three short. It can be sent by light, sound, or any other signalling method. A safe water mark often uses Morse A, which is dot dash. A Yachtmaster should recognise these common Morse patterns even if they cannot send fluent Morse.
Sound signals are not only for fog. COLREGs include manoeuvring and warning signals in sight of other vessels, such as one short blast for altering course to starboard, two short blasts for port, three short blasts for operating astern propulsion, and five or more short blasts for doubt or danger.
Avoid mixing a buoy light with a vessel signal
At night the lookout sees a white short-long flash near the expected safe-water mark while a power-driven vessel in sight sounds one short blast.
1. Classify the source
Decide whether the observation comes from an aid to navigation, a vessel or a distress transmission.
2. Use the rule context
Morse A supports safe-water-mark identification; one short blast communicates alteration to starboard in sight of another vessel.
3. Cross-check
Confirm the buoy by charted position and other characteristics, and continue collision assessment of the vessel.
Sense check: The crew does not treat the same dot/dash vocabulary as one universal meaning across buoyage, distress and COLREG traffic.
Common mistake or limitation
- One or two short manoeuvring blasts are Rule 34 signals for vessels in sight, not a fog rule for an unseen target.
- Morse A is one clue to a safe-water mark; charted position, colour and full light character still need to agree.
- Five or more short rapid blasts express doubt or danger; they do not give the other vessel a collision-avoidance instruction.
- SOS is a recognised distress signal, but available radio or beacon alerting and an accurate position remain essential.
Recap
- SOS — three short, three long, three short; recognised distress.
- Morse A — short-long; commonly used by a safe-water mark.
- One/two/three short blasts in sight — starboard/port/astern propulsion indications.
- Five or more short rapid blasts — doubt or danger.
Optional quick check
Section 8 of 18
You hear one short blast from a vessel you can see. Which interpretation is correct?
Sources and factual review
Reviewed 20 August 2026 - Compass Revision editorial review.
Continue studying Signals & Communications
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